Trace Elements Characterization in Fresh and Composted Livestock Manures

Animal manure is identified as the alternative of fertilizers to enhance the soil fertility and crop production. But the application of animal manure may contaminate the environment with heavy metals; thus it is imperative to determine the heavy metal contents of manures. The present study was aimed to compare the trace elements in fresh and composted animal manures using the sequential fractionation method. Composted and fresh animal manures from four different animals, [buffalo (BF), cow fresh (CW), goat (GT) and poultry (PL)], were selected to determine various fractions of iron (Fe), zinc (Zn), nickel (Ni), manganese (Mn) and mercury (Hg). Metals were stepwise fractionated into exchangeable, adsorbed, organically bound, carbonate precipitated and residual forms. The extractability of elements considerably varied depending on the type of livestock and extraction method. The composted and fresh manure exhibited the lower concentrations of water soluble extractable metals as compared to other fractions. A great proportion of metal was detected in carbonate and residual forms. Irrespective of the form of element, the reagents were varied in order of HNO3> EDTA >NaOH> KNO3> H2O, while metal species were found in the order of Fe> Hg >Mn> Zn > Ni. Iron, Mn and Hg were found in higher concentration in composted manures whereas Ni and Zn concentrations were sparingly higher in fresh manures. Analytical results indicated that composting of animal manures might have encouraged soil microbial activity, which promoted trace mineral supply thus improving the plant nutrition. The variations in the heavy metals could be related to the chemical properties of the individual metals and the characteristics of manure.